The present invention relates to the field of cooling systems for a hybrid powertrain of a motor vehicle.
A hybrid drive vehicle or hybrid traction vehicle is provided with a first drive source and/or an electricity generator comprising an internal combustion engine and a second drive source and/or a source of transforming electrical energy into mechanical energy implemented by one or more electric motors. It is possible, for example, to have two electric motors powered by a battery and each positioned in the region of a rear wheel of the motor vehicle. Such electric motors are generally called “wheel motors”.
The internal combustion engine and the electric motors as well as the electronic power components controlling the operation of the electric motors do not require the same degree of cooling to operate in optimal conditions. The temperature ranges of the heat transfer fluids circulating in the cooling circuits of the different elements are not the same. Thus, the temperature of the coolant at the inlet of the various electronic components must not exceed 80° C., while the temperature at the inlet of the electric motor must not exceed 90° C. and that at the inlet of the internal combustion engine is limited to 105° C.
To resolve the problems resulting from these differences in temperature, it is possible to use separate cooling circuits. A first circuit is thus used for cooling the internal combustion engine. This circuit corresponds to a conventional cooling circuit of an internal combustion engine in a conventional vehicle and is provided with a first radiator. A second circuit may thus be provided for cooling the electric traction assembly or electric powertrain comprising at least one electric motor and various electronic power components.
Such a cooling system has a first drawback, in that the circulation pump of the second cooling circuit of the electric traction assembly has to operate continuously. A further drawback is due to the position of the radiator of the second cooling circuit which is generally placed upstream of the radiator of the first cooling circuit, thus causing additional pressure losses in the flow of cooling air.
A further solution consists in using a cooling circuit which is common to the internal combustion engine and the electric traction assembly. The cooling circuit of the internal combustion engine at high temperature, between 90 and 115° C., is used to cool the electric components of the electric traction assembly at lower temperatures, between 70 and 80° C. Such a cooling system uses a single radiator comprising an inlet and two outlets.
Reference may be made in this regard to the French patent application 2 844 224 (Renault) which discloses the use of a single cooling circuit permitting two temperature levels to be provided for the heat transfer fluid, on the one hand, for cooling the internal combustion engine at a high temperature, for example 90 to 115° C. and, on the other hand, for cooling the components of the electric traction assembly at a lower temperature, for example 70 to 80° C. The cooling system comprises a single radiator having a single inlet and two outlets so as to define a main circuit and an auxiliary circuit. A two-way electrostatic valve associated with a three-way thermostatic valve makes it possible to control the entire cooling system and to obtain for the heat transfer fluid the temperatures required both for the internal combustion engine and for the components of the electric traction assembly. However, the two-way thermostatic valve has to be placed in the cooling circuit at a specific location and has to be designed so as to open at relatively low temperatures. The adaptation of such a structure to a cooling system of a vehicle with a hybrid powertrain results in significant costs.
However, the flow of the heat transfer fluid in such a structure depends on the temperature of the fluid and not on the dynamic conditions of the motor vehicle, which does not enable the consumption of fuel and the performance of the electric motor to be optimized.